Leukotrienes are metabolites of arachidonic acid through the 5′-lipoxygenase pathway and are important mediators of allergic response, such as that involved in bronchial asthma. Drugs that exert antagonistic effects on the leukotrienes are useful for the treatment of allergic diseases.
The synthesis and biological activity of many phenoxyalkylcarboxylic acid derivatives, which are leukotriene antagonists, are described by Ohashi et al., U.S. Pat. No. 4,985,585. The compounds were obtained in laboratory scale amounts by silica-gel column chromatography of the crude product mixtures. The solvent was evaporated to give either a pale yellow oil or colorless crystals and no deliberate effort was made to control crystal morphology.
We have observed that 4-[6-acetyl-3-[3-(4-acetyl-3-hydroxy-2-propylphenylthio)propoxy]-2-propylphenoxy]butyric acid (1), which is Example 33 in Ohashi et al., is orally active for treatment of asthma and allergic diseases and that the solid compound can crystallize into several distinct polymorphs when prepared in bulk.
It has been discovered that the crystallization conditions, particularly temperature, is critically important for preparing the different polymorphs.

We have also found that the solubility and the bioavailability of one of these polymorphs, identified as orthorhombic crystals (Form V in Table 1, and Form A in FIG. 6), is superior to the other polymorphs and thus form A offers improved solid formulations.